Various types of vehicles are known which transport shaking devices or "heads" from tree to tree within fruit or nut orchards. The design of most vehicular orchard harvesters is such that the shaking device or "head" may be brought into a gripping relationship with a limb or trunk of a tree only through rather careful maneuvering and precise positioning of the transport vehicle. Other vehicular orchard harvesters include a positioning apparatus which, once the vehicle is proximal to a tree trunk or limb, is operated to bring the shaker head into gripping relationship with the appendage.
However, the freedom of movement of the positioning apparatus is necessarily limited to a small zone closely adjacent to the initial position of the head. Therefore, a great deal of effort has been directed to expanding the maneuverability of the vehicle itself so that the head may be quickly positioned close enough to a tree that minimal adjustment of the head is needed to grip the tree.
Prior art vehicles have been divided into two classes: those that are adapted generally for movement along a line of advance which is parallel to a row of trees, i.e. normal to axes extending radially from the center of a tree; and those that maneuver best by approaching each individual tree head-on, i.e. advance and recede along said radial axes.
The latter "in-and-out" type of vehicle is illustrated in U.S. Pat. No. 4,409,782 to Westergaard et al. That device includes a three wheeled harvester vehicle having two front wheels fixed in position for parallel rotation about a single axis normal to the line of advance and a dirigible or steering rear wheel which rotates about an axis generally parallel to the axis of the front wheels. Head positioning apparatus extends longitudinally outwardly from the front of the vehicle. The vehicle is moved radially inward toward the tree so that the trunk thereof may be grasped by the jaws of the head clamping assembly.
After the tree has been gripped and shaken so that fruit falls onto the ground or into a catching frame, this type of vehicle reverses direction and moves outward on generally the same radial horizontal axis as was used for approach. If on the initial try the head is not close enough to the trunk or limb to be moved in place by the positioning apparatus, then the vehicle must back away from the tree and re-approach. This is an inefficient maneuver from the point of view of time and operator effort.
It is a significant problem that various ground contacting pieces of vehicular apparatus used in the conduct of orchard tree culture are run in close proximity to fruit and nut trees, thereby contributing to additive compaction of the soil surrounding the trees. As most orchard culture methods minimize soil tillage, any compaction becomes a permanent degradation of orchard quality. Compaction decreases the ability of tree root systems to expand and, as well, to absorb essential water and nutrients. The compaction problem is exacerbated by use of vehicular orchard shakers which must, as in the case of in-and-out vehicles, pass over the same ground repeatedly to position the shaking head on the tree.
"Down-the-row" types of shakers generally include a shaker head which is mounted to a carriage capable of inward and outward movement relative to the vehicle along a path transverse to the line of advance of the vehicle, as in U.S. Pat. No. 4,223,515 to Borchard. Another similar vehicle is shown in the patent to Toet, U.S. Pat. No. 3,706,187. The latter vehicle shows a three-wheeled arrangement not unlike that of Westergaard except that the single wheel is on the front, rather than the rear, and all three wheels are steerable. However, this vehicle is advanced parallel to the row of trees. Once it is positioned with its axis of travel perpendicular to an axis extending radially outward from the center of the tree, a laterally extending head engages the tree. After the tree has been shaken, the vehicle moves down the row to a position normal to a horizontal radially extending axis of the next tree. While it is not often necessary to back up such a vehicle, a precise line of travel must be maintained from tree to tree if the shaker head is to continue to come to rest in a grippable zone of adjustment when the vehicle is stopped. The length of such vehicles renders it impractical or impossible to encircle an individual tree.
It will be appreciated from the foregoing that a vehicle is needed which is highly maneuverable within a generally circular zone having a tree trunk as its center and also along a straight path of advance parallel to a row of orchard trees. Such a vehicle must be balanced so as to safely carry bulky head positioning and shaking assemblies. It must also be compact enough to accomplish such maneuvers within the tightly confined space of a densely planted fruit or nut orchard.